The invention concerns a process for the production of an aromate concentrate suitable for use as blending component for gasifier fuel, from feed hydrocarbon mixtures having a boiling range from between 40.degree. to 170.degree. C., containing in addition to non-aromates, several aromates, whereby the feed hydrocarbon mixture is subjected to an extractive distillation using N-substituted morpholines, substituents of which display no more than seven C-atoms, as selective solvent, and whereby the low-boiling non-aromates with a boiling range up to about 105.degree. C. practically completely and the higher boiling non-aromates with a boiling range between about 105.degree. and 160.degree. C. predominantly are distilled off as raffinate across the top from the extractive distillation column, whereas the major amount of aromates as well as the residual non-aromates, together with the employed solvent, are discharged as extract from the sump of the extractive distillation column, whereupon the solvent is separated from the other hydrocarbons of the extract, distillatively, in a subsequently disposed solvent stripping column, and these other hydrocarbons are employed partially or completely as blending component.
A process of this type, which is not however considered state of the art, is described in DE-OS 36 12 384. This reference suggests that the feed hydrocarbon mixture is to be led into the extractive distillation column without previous separation into individual fractions.
Particularly suitable feed hydrocarbon mixtures are disclosed to be the so-called reformate and platformate from the working-up of petroleum, with not too high a content of benzene. One can, however, also employ mixtures of such reformate and platformate with pyrolysis benzenes.
Normally, the end of boiling of these entry products lies at about 170.degree. C. In practice, however, it has turned out that this boiling end level is not maintained in many cases, since the above-described production processes causes a formation of condensation and polymerization products, which display a higher boiling point than 170.degree. C. and which, accordingly, contaminate the reformate and platformate. Since these higher boiling condensation and polymerization products are often present in the reformate and platformate in concentrations up to about 30% by weight, they can lead to considerable impairment in performance of the processes described in DE-OS 36 12 384.
In practice, it has been proven that, namely, these condensation and polymerization products concentrate in the selective solvent, since they can only be distillatively separated from them practically not at all or incompletely. With increasing operational time, this leads to an increasingly stronger contamination of the solvent led in circulation, whereby its selectivity progressively decreases and the separation effect in the extractive distillation diminishes correspondingly.
Attempts to separate these condensation and polymerization products by means of distillation of the solvent have--as already mentioned--provided no satisfactory results, even with use of a high distillation expenditure. It has been proven, namely, that part of these condensation and polymerization products have a corresponding boiling range as the solvent, so that a distillative separation is practically impossible. Accordingly, this problem could previously be solved only by undergoing a complete exchange of the contaminated solvent after a certain period of operation. On the one hand, this technique is extremely costly and thereby impractical. On the other hand, destruction of the contaminated solvent necessitates additional costs, since it can no longer be introduced to any other employment or utilization.
The invention is therefore based upon the object of so improving the older process that the above-depicted disadvantages can be avoided.